. 2020 Sep 11;119(8):1538–1549. doi: 10.1016/j.bpj.2020.08.038

Table 2.

Reactions and Kinetic Parameters for the Cochaperone Aha1

No.	Reaction	k_f	k_r
23a	H90_open + Aha1 $⇌$ Aha1⋅H90_open	1 μM⁻¹ s⁻¹	1.2 s⁻¹
23n	$H 90_{o p e n}^{A T P} + A h a 1 ⇌ A h a 1 \cdot H 90_{o p e n}^{A T P}$	Same as 1a	Same as 1a
24	$H 90_{c l o s e d}^{A T P} + A h a 1 ⇌ A h a 1 \cdot H 90_{c l o s e d}^{A T P}$	1 μM⁻¹ s⁻¹	1.6 × 10⁻¹ s⁻¹
25	$A h a 1 \cdot H 90_{o p e n}^{A T P} ⇌ A h a 1 \cdot H 90_{c l o s e d}^{A T P}$	1.7 × 10⁻¹ s⁻¹	6.67 × 10⁻⁵ s⁻¹
26d	$d \cdot A h a 1 \cdot H 90_{o p e n}^{A T P} ⇌ d \cdot A h a 1 \cdot H 90_{c l o s e d}^{A T P}$	Max (25 and 11d)	From 11d, 23n, 24
26m	$m \cdot A h a 1 \cdot H 90_{o p e n}^{A T P} ⇌ m \cdot A h a 1 \cdot H 90_{c l o s e d}^{A T P}$	Max (25 and 11m)	From 11m, 23n, 24

The dissociation rate constants are computed from the binding affinities measured by surface plasmon resonance (35). I assume that Aha1 accelerates the closure of the Hsp90 dimer by 10-fold (51). The rate of client-bound Hsp90 dimer closure in the presence of Aha1 (reactions 26d, 26m) is given by the larger k_f of the reaction 11d and of the reaction 25; the reverse rate is computed from the reaction cycle of the indicated reactions.